CVE-2026-89478

In the Linux kernel, the following vulnerability has been resolved:

sctp: drop a chunk if its transport was removed

sctp rcv() resolves the transport once per packet and leaves it in chunk->transport. The lookup reference, or the one sctp add backlog() takes if the socket is owned by userspace, keeps it around until the chunk has been processed.

An authenticated ASCONF DEL-IP can remove it in the meantime. sctp assoc rm peer() takes the transport out of the association and calls sctp transport free(), which tags it dead and drops the reference the association held. There is a window on both paths: the packet can sit on the socket backlog, and on the direct path the lookup completes before bh lock sock().

The DATA chunk in that packet puts the removed transport back into asoc->peer.last data from. Once the packet is done that reference goes away and the transport is freed by RCU, so the next delayed SACK carries the pointer into the SACK chunk and sctp outq select transport() reads the freed transport's state.

Drop the chunk in sctp inq push(), next to the existing rcvr->dead check. Both paths reach it with the association's socket lock held. The peer retransmits it.